Recent years have witnessed practical use of a flat-panel display in various products and fields. This has led to a demand for a flat-panel display that is larger in size, achieves higher image quality, and consumes less power.
Under such circumstances, great attention has been drawn to an organic EL display device that (i) includes an organic EL element which uses electroluminescence (hereinafter abbreviated to “EL”) of an organic material and that (ii) is an all-solid-state flat-panel display which is excellent in, for example, low-voltage driving, high-speed response, and self-emitting characteristics.
An organic EL display device includes, for example, (i) a substrate made up of members such as a glass substrate and TFTs (thin film transistors) provided to the glass substrate and (ii) organic EL elements provided on the substrate and connected to the TFTs.
An organic EL element is a light-emitting element capable of high-luminance light emission based on low-voltage direct-current driving, and includes in its structure a first electrode, an organic EL layer, and a second electrode stacked on top of one another in that order, the first electrode being connected to a TFT.
The organic EL layer between the first electrode and the second electrode is an organic layer including a stack of layers such as a hole injection layer, a hole transfer layer, an electron blocking layer, a luminescent layer, a hole blocking layer, an electron transfer layer, and an electron injection layer.
A full-color organic EL display device typically includes, as sub-pixels aligned on a substrate, organic EL elements of red (R), green (G), and blue (B). The full-color organic EL display device carries out an image display by, with use of TFTs, selectively causing the organic EL elements to each emit light with a desired luminance.
The organic EL elements in a light-emitting section of such an organic EL display device is generally formed by multilayer vapor deposition of organic films. In production of an organic EL display device, it is necessary to form, for each organic EL element that is a light-emitting element, at least a luminescent layer of a predetermined pattern made of an organic luminescent material which emits light of the colors.
In formation of films in a predetermined pattern by multilayer vapor deposition, a method such as a vapor deposition method that uses a mask referred to as a shadow mask, an inkjet method or a laser transfer method is applicable. Among these methods, the vapor deposition method that uses a mask referred to as a shadow mask is the most common method.
In a vapor deposition method employing a mask called a shadow mask, a vapor deposition source that evaporates or sublimates a vapor deposition material is provided in a chamber inside which a reduced-pressure condition can be maintained. Then, for example, under a high-vacuum condition, the vapor deposition source is heated, and thereby the vapor deposition material is evaporated or sublimated.
Thus evaporated or sublimated vapor deposition material is vapor-deposited, as vapor deposition particles, onto a film formation target substrate onto which a film is to be formed. This vapor deposition is carried out through apertures provided to the mask for vapor deposition, so that a desired film pattern is formed.
However, in such a case of vapor deposition by evaporation or sublimation of a vapor deposition material, that portion of the vapor deposition material which has adhered to or has accumulated on a place other than the film formation target substrate end up as a material loss unless it is recovered.
In particular, an organic material that constitutes such an organic EL layer as that described above is a special functional material having electric conductivity, a carrier-transporting property, a light-emitting property, thermal and electrical stability, etc., and the unit price of such a material is vary high.
For this reason, in order to improve efficiency in the use of material, it is desirable to recover and reuse that portion of the vapor deposition material which has adhered to a place other than the film formation target substrate.
Note that the term “efficiency in the use of material” refers to the ratio of that portion of a vapor deposition material for use in vapor deposition which is actually utilized.
Patent Literature 1 discloses a vapor deposition apparatus and a vapor deposition method for reducing an amount of a vapor deposition material that accumulates on a place other than a film formation target substrate, and for recovering and reusing that portion of the vapor deposition material which has accumulated on a place other than the film formation target substrate.
FIG. 19 is a cross-sectional view schematically showing a vacuum vapor deposition apparatus as described in Patent Literature 1.
The vapor deposition apparatus 500 described in Patent Literature 1 includes: a vapor deposition source 501; a vapor outlet 502 serving as an emission hole of the vapor deposition source 501; and a vapor deposition material recovery tool 510 which includes a barrier 511 surrounding the vapor outlet 502 and a vapor flow release outlet 512 facing the vapor outlet 502 and which serves as a cover member that covers the vapor outlet 502.
The barrier 511 has its inner surface spherically concaved, with the vapor flow release outlet 512 formed at the top thereof.
Placed above the vapor deposition source 501 are a film formation target substrate 200 and a vapor deposition mask 531. Note that in Patent Literature 1, the mask 531 is placed over a predetermined position on a film formation target surface of the film formation target substrate 200.
According to Patent Literature 1, a vapor deposition material having accumulated on the barrier 511 is recovered by taking the vapor deposition material recovery tool 510 out of a vapor deposition chamber 521 after performing vapor deposition while controlling an angle of divergence of a vapor flow (vapor deposition flow) that flows from the vapor deposition source 501 toward the film formation target substrate 200.
According to Patent Literature 1, only that portion of the vapor flow emitted through the vapor outlet 502 which has passed through the vapor flow release outlet 512 is supplied toward the film formation target substrate 200, and that portion of the vapor flow which flow toward the barrier 511 stays within the vapor deposition recovery tool 510.
This makes it possible, with the vapor deposition material recovery tool 510, to recover that portion of the vapor flow emitted through the vapor outlet 502 which has passed flows toward a place other than the film formation target substrate 200, thus making it possible, by reusing the vapor deposition material thus recovered, to increase the efficiency in the use of material.